With respect to rollers for preparing the ground of roadbed and pavement, hand guide rollers are among the relatively small sized rollers that are known. Such rollers are in demand because of their simple structure. Because of their small size, the steering is manual by pushing and pulling the handle manually in a horizontal direction by human power.
The structure as shown in FIG. 5 has been widely used as hand guide rollers. Front and a rear rollers 4, 5 are supported by a frame, and a handle bar 9 is secured at the rear side of the frame. Within the frame, a single vibration generator (not shown) is provided to transmit vibration to the front and rear rollers 4, 5 through the frame. Advancing directions are, as shown in the drawing, changed by pushing and pulling the handle bar 9 manually in horizontal (i.e., lateral) directions to steer the front and rear rollers 4, 5 together with the frame. Because this structure is satisfactory with a single vibration generator and is not provided with a steering mechanism, it is very simple and economical in production cost. Thus, such a structure is quite a suitable hand guide roller.
However, in this structure, when steering, the entire guide roller must be moved as a whole. As such, to push and pull the handle requires a certain amount of physical strength. Accordingly, structures have been provided with a steering mechanism, and results in the saving of labor.
There are several types of steering mechanisms. One type, type (1) is a mechanism or structure that turns either one of the front and rear rollers with a turning axis positioned at the center of the roller. Another type, type (2) is a mechanism or structure that concurrently turns both the front and rear rollers with turning axes disposed at both rollers. A third type (3) is a mechanism or structure where the frame for supporting the front and rear rollers is divided into two, forwardly and rearwardly, and the divided frames are pivoted at the center of the roller car.
Comparing these three steering mechanisms, type (1) has the disadvantage that there is a large difference in the inner track between the front and rear rollers during turning, and the running or traveling loci are greatly diverged between the front and rear wheels. Type (2) has the disadvantage that two turning axes are necessary resulting in a complicated structure and high costs. By comparison, the type (3) structure is assumed to be the most suitable, but also has disadvantages as discussed below.
First, in the type (3) structure, the pivoting of the front and rear supporting frames is along a turning axis and bearing which are opposed in a vertical direction. Thus, the height of the car is inevitably tall which is not preferred for a hand guide roller that requires compactness.
Also, when providing a single vibration generator, because vibration is transmitted to at least either of the front and rear rollers through the axis, the turning axis and the bearing must be of high strength, which has a high cost. On the other hand, if separate respective vibrators are disposed in respective interiors of the rollers, as in large sized guide rollers, members of high strength are not necessary, but two vibrators are required, as well as a structure for synchronizing both vibrators. This also results in high costs.
Moreover, with an axis and bearing, the large rattling that would occur requires high precision which is difficult to produce and durability is a concern.
The present invention has been devised in view of problems involved with the prior art, and accordingly it is an object to offer such a hand guide roller which is easy in steering, compact in the structure, and low in production cost.